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SubjectRe: [PATCH 2/9] blkcg: drop unnecessary RCU locking
On Fri, Feb 17, 2012 at 11:47:49AM -0500, Vivek Goyal wrote:
> So now in some cases we call blkg_lookup_create() with both queue and rcu
> read lock held (cfq_lookup_create_cfqg()) and in this case hold only queue
> lock.

So, this should be okay. It's currently not because blkg_alloc() is
broken due to percpu allocation but other than that calling both w/
and w/o RCU read lock should be fine.

> blkg_lookup_create() calls blkg_lookup() which expects a rcu_read_lock()
> to be held and we will be travesing that list without rcu_read_lock()
> held. Isn't that a problem?

No, why would it be a problem?

> We might be examining a blkg belonging to a different queue and it
> might be being freed parallely.

How?

Thanks.

--
tejun


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